Interference in cellular networks is one of the most common problems in radio access networks. In frequency division duplex (FDD) cellular systems, both the receiver and transmitter are active at the same time. As a result, a transmit (Tx) signal from the transmitter leaks into the receiver causing interference in a receive (Rx) signal from an antenna. The interference can result in dropped calls, decreased receiver sensitivity (and range), increased Rx noise figure and desensitization of receive-system active components.
To prevent the Tx signal from leaking into the transmitter, in some topologies, high-performance filters are used in the front end. However, the high-performance filters at the front end incur significant cost for an original equipment manufacturer (OEM). To reduce the cost, it has been proposed that expensive filters be replaced by using low cost filters and their performance augmented by using self-interference cancellation. Proposals for using self-interference cancellation, have so far been approached by using predetermined cancellation parameters (such as amplitude and phase shift) to cancel out the interference in the Rx signal. However, with changes in environment conditions, there will be variations in the interference in the Rx signal and these topologies do not address the issue of maintaining the cancellation with the changes in the environment conditions. In particular, temperature changes and proximity of antennas to a hand, head, or other objects can cause large variation in voltage standing wave ratio (VSWR) at the antenna resulting in amplitude or phase changes in the interfering signal to be cancelled.